1. Technical Field
The present invention relates to a control device of a fan motor that is capable of suppressing a loss of a drive circuit to be a certain value or less even if an input voltage of the fan motor is changed.
2. Description of Related Art
In the related art, for a fan motor, a brushless motor capable of performing speed control over a wide range of speeds is used. The brushless motor includes a plurality of Hall elements as disclosed in Japanese Unexamined Patent Application Publication No. 2006-180608. A control device of the fan motor operates a drive circuit and rotates the brushless motor using a signal output from the Hall elements.
Typically, in a working voltage of the brushless motor, a rated voltage, an upper limit voltage, and a lower limit voltage around the rated voltage are determined. The upper limit voltage of the brushless motor is determined to be a voltage that is less than a permissible loss of the drive circuit built in the brushless motor. Furthermore, air volume-static pressure characteristics when the brushless motor is operated at the rated voltage are also determined.
However, in the control device of the fan motor of the related art, if the input voltage is changed, the input voltage of the brushless motor is also changed. Thus, in order not to exceed the permissible loss of the drive circuit, the rated voltage is inevitably set to be considerably lower than the upper limit voltage. Therefore, it is difficult to further improve the air volume-static pressure characteristics at the rated voltage.